Field of the Invention
The invention relates to an electronic entity with integrated coupling between a microcircuit and an antenna, in particular an electronic entity having a dual interface, i.e. an entity comprising, on the one hand, a module for communicating by contact and, on the other hand, a body in which the module is incorporated and that is equipped with an antenna for contactless communication. Such an entity may be a microcircuit card as defined by ISO-7816.
Description of the Related Art
Conventionally, an entity having such a dual interface comprises two electromagnetic coupling coils (or antennas) that are respectively located in the plane of the antenna and on the module; in FIG. 1, the module 10A is shown diagrammatically by the component on the right, comprising a microcircuit 11 and a coupling coil (there are additionally contacts for connecting to an external reader, but for the sake of simplicity, these are not shown), while the body 10B is shown diagrammatically on the left with an antenna 13 that is connected, via a capacitor 14, to a second coupling coil 15. The quality of the connection between the microcircuit and the antenna depends on the quality of the coupling between the coils 12 and 15.
Such a configuration is, for example, described in the document U.S. Pat. No. 6,378,774 (or its European equivalent, EP-1 031 939) relating to a microcircuit card. The module therein is, as is conventional, formed from a carrier film having a first face, called the outer face, comprising contact areas, and a second face, called the inner face, fixed to which is a microcircuit connected to the contact areas through the carrier film. The card body therein comprises a carrier sheet on which, on the one hand, the antenna and, on the other hand, the other coupling coil are formed, which may be equally on the outside of the antenna as on the inside thereof; the card body is formed by the injection molding, on both sides of the carrier sheet, of a material that, in practice, is similar to that of this sheet; in the body thus formed a cavity is then formed in which the module is fixed; the coupling coil formed on the carrier sheet is localized there so as to be in proximity of the coil of the module when this module is fixed in this cavity. According to one embodiment, the position for the carrier sheet is located below the cavity and the coupling coil borne by the module is formed on this second face; the gap between the two coupling coils is then of the order of magnitude of the depth of the cavity. In another embodiment, the coil borne by the module is wound around the microcircuit and the cavity passes through, at least partly, the carrier sheet of the antenna; the coupling coil formed in this carrier sheet is then located approximately at the same depth as the coupling coil of the module, but laterally removed therefrom.
According to yet another embodiment (see the document EP-2 525 304), the coupling coil located in the plan of the antenna may be formed by a portion of this antenna which is locally shaped in a suitable manner.
In practice, two ways for forming a card body (and more generally for forming the body of an electronic entity) are known; either by overmolding (in practice by injection molding) over a carrier sheet, as proposed in the aforementioned documents U.S. Pat. No. 6,378,774 or EP-1 031 939), or by lamination of a plurality of layers (see the diagram of FIG. 2), namely two (optional) compensating layers 27A and 27B to compensate for local variations in thickness resulting from the formation of the antenna 23 and of the associated coupling coil 25 on the carrier sheet 26, two core layers 28A and 28B that are located respectively on either side of the carrier sheet (and of potential compensating layers) and bearing the visual patterns intended for the card, and two covering layers 29A and 29B ensuring the protection of the underlying layers.
In practice, the carrier sheet 26 may be made of polyethylene terephthalate (PET for short), but may also be produced from a material such as polyvinyl chloride (or PVC) or polycarbonate (or PC for short): these are generally rigid materials. The compensating layers 27A and/or 27B may be formed from one of the aforementioned materials, as may the core layers; if these layers are formed from one and the same material, the interfaces between these layers may be hardly detectable. The covering layers, the function of which is mainly to protect the underlying layers, are often transparent.
The various known solutions are generally complex to implement (numerous layers, or overmolding by injection; restrictions in the choice of the materials considering the deposition-etching operations conventionally used; formation of the coil around the microcircuit, etc.) and do not allow both a small distance between the coupling coils (hence an effective coupling) and good reproducibility of this relative configuration between these coupling coils to be obtained.
On this subject, it may be recalled that:                the tolerances for positioning the antenna on the carrier sheet are typically of the order of 0.5 mm,        the tolerances for printing the visual patterns are typically of the order of 0.1 to 0.2 mm,        the tolerances for superposing the stack of layers are typically of the order of 0.2 to 0.3 mm,        the laminating tolerances are typically of the order of 0.1 to 0.2 mm,        the punching tolerances (for delimiting the outline of the card body) are typically of the order of 0.3 to 0.5 mm        the tolerances for machining the cavity are typically of the order of 0.05 mm and        the tolerances for inserting the module into the cavity are typically of the order of 0.05 mm.        
It is therefore no exaggeration to conclude that the overall tolerances, in terms of root mean square, are of the order of a millimeter.
It will be understood that such drawbacks in terms of complexity and imprecision in the distance between coupling coils may be observed independently of the fact that the electronic entity effectively has one interface for external communication by contact.